1. Field of the Invention
The present invention relates to an apparatus for supplying a constant quantity of abrasive, and in more detail relates to an apparatus in a blasting machine for controlling to keep a quantity of adhesive in a constant quantity to be ejected from a blast gun or nozzle of the blasting machine as for a mixture of a compressed fluid such as compressed air or gas and abrasive using the blast gun.
2. Description of the Related Art
In a blasting machine for ejecting a mixed fluid of compressed gas and abrasive, if fluctuations arise in the quantity of abrasive to be ejected, a precision of machining of a workpiece will vary due to fluctuations of degree in the processing. Thus, there has been proposed an apparatus for supplying a constant quantity of abrasive for obtaining a mixed fluid by supplying a constant quantity of abrasive with a compressed fluid to be ejected from a blast gun, so as to make the abrasive to be ejected always a constant quantity.
An example of such an apparatus for supplying a constant quantity of abrasive will be described taking the apparatus used in a suction type blasting machine as an example, with reference to FIG. 5 and FIG. 6.
The suction type blasting machine is provided with a conduit for compressed air 46 inside a blast gun, and a branched conduit 42 branching from this conduit 46, as shown in FIG. 5, and if high pressure compressed air is supplied to the inside of the conduit for compressed air 46, abrasive is sucked via the branched conduit 42 by the suction force (suction negative pressure) generated at that time, and ejected together with the compressed air. An apparatus for supplying a constant quantity of abrasive 1 used in this type of the suction blasting machine is provided with an abrasive conduit 44, which is a branched conduit converging with the previously described conduit for compressed air 46, an abrasive tank 10 that is communicated with the abrasive conduit 44, and means for supplying abrasive inside the abrasive tank 10 to the abrasive conduit 44.
As this means for supplying a constant quantity of abrasive inside the abrasive tank 10 to the abrasive piping 44 at a time, with the apparatus for supplying a constant quantity of abrasive 1 shown in FIG. 5 and FIG. 6, a drum 50 having a plurality of V-shaped grooves 47 formed on an outer surface is rotatably housed in a state immersed in abrasive inside the abrasive tank 10 such that the peripheral surface of the drum 50 is partially exposed above the abrasive, and by arranging one end 45 of the abrasive conduit 44 facing the grooves 47 at the outer periphery of the drum 50 exposed above the abrasive, abrasive that has been collected inside the grooves 47 by rotation of the drum 50 is sucked into the abrasive conduit 44, is mixed with compressed air flowing in the conduit for compressed air 46, then ejected from the tip of a blast gun (not shown).
Accordingly, by controlling the rotational speed of an electric motor 30 for rotational drive of the drum 50 using an inverter, for example, it is possible to control a quantity of abrasive to be ejected in accordance with variation in this rotational speed (Japanese Unexamined Patent Publication No. Hei. 9-38864; hereinafter referred to as “864”).
Also, in the case where this type of apparatus for supplying a constant quantity of abrasive is utilized in a direct pressure type blasting machine, then as shown in FIG. 7, a drum 50 with a plurality of rectangular indented sections 49 for measuring a constant quantity of abrasive at a time, formed on an outer periphery is arranged inside an abrasive tank 10, one end of an abrasive conduit 44, having other end 45 opening to the indented sections 49 provided on the drum 50, communicates with a conduit for compressed air 46 (here, also used as a mixed fluid conduit) in which compressed air that will be ejected from the tip of a blast gun (not shown) flows, with a duct 43 being further provided in the abrasive conduit 44, for supplying compressed air to the abrasive conduit 44, and by sucking compressed air into the indented sections 49 using the compressed air supplied via the duct 43 to the abrasive conduit 44 to blow the abrasive that has been collected in the indented section 49 upwards and mix it with compressed air flowing in the conduit for compressed air 46, it is possible to eject a constant quantity of abrasive together with compressed air from the blast gun at a time.
With the apparatus for supplying a constant quantity of abrasive 1 used in this direct pressure type blasting machine also, similarly to that for the previously described suction type blasting machine, it is possible to control the quantity of abrasive to be ejected from the blast gun by controlling the rotational speed of a motor for turning the drum 50 using an inverter or the like (Japanese unexamined patent No. Hei. 11-347946; hereinafter referred to as “'946”).
An apparatus for supplying a constant quantity of abrasive has also been proposed in which instead of the indented sections for measuring abrasive in '946, holes passing through in the thickness direction of a rotating disk are formed, making it possible to collect abrasive inside these holes (Japanese unexamined patent No. 10-249732; hereinafter referred to as “'732”).
With respect to the apparatus for supplying a constant quantity of abrasives 1 of the related art as described above, in the case of said apparatus 1 disclosed in '864 and '946 cited above, both have abrasive measurement carried out by bottomed rectangular grooves 47 or indented sections 49 formed on the outer periphery of a drum 50, but even if such grooves 47 or indented sections 49 are formed anywhere over the entire periphery of the drum 50, it is necessary to have extremely high machining accuracy in forming them to a uniform depth. For this reason, formation differences in the grooves 47 and indented section 49 occurring at the time of manufacture will be a direct cause of errors in the quantity of measured abrasive.
However, particularly with the indented sections 49 as shown in '946 cited above, in the event that that they are formed as comparatively deeper holes with the bottoms, it is difficult for abrasive to enter into the inside of the holes, and as well as variations arising in the quantity of abrasive collected inside each indented section 49, there may be cases where once abrasive goes in to an inside of the indented section 49, it is impossible to extract all of the abrasive by blowing compressed air, and the quantity of abrasive collected inside each of the indented section 49 being a constant quantity, and the abrasive extracted from the indented sections 49 being a constant quantity, inherently have low reliability.
This point, although not shown in the drawings, is because with the apparatus for supplying a constant quantity of abrasive 1 disclosed in '732 cited above, hole sections passing through a circular disk in a thickness direction are provided, and measurement of the abrasive is performed with these hole sections, which means that if the disk thickness is constant, the depth (length) of the formed holes can be made constant, and compared to the previously described case of the holes with bottoms, it is easier to get the abrasive to flow and to get it out again.
However, even if no error in quantity of abrasive arises between each hole section, there are cases where an insufficient quantity of abrasive enters into the hole sections, or where even when a required quantity of abrasive has been collected inside the hole section, the abrasive falls out of the grooves 47 or hole sections after collection while being supplied to the abrasive conduit 44, and in the related art structures, there is no provision of a structure for ensuring a constant quantity of abrasive is finally supplied to the abrasive conduit 44.
With the above described structures of the related art also, in order to prevent insufficient abrasive entering the grooves 47 and the indented sections 49, it has been proposed to have a structure that subjects the abrasive tank 10 and the drum 50 to vibration to make it easy for abrasive to enter the grooves 47 or the like and makes it possible for surplus abrasive that is overflowing from the grooves 47 or the like to be shaken off (in '864 cited above), but in the event that the abrasive tank 10 is vibrated in this way, bridges where the abrasive has compacted may occur inside the abrasive tank 10, which adversely lowers fluidity.
When abrasive is shaken out, it has once entered in the grooves 47 by the vibration of the abrasive tank 10 and drum 50 in this way, and constant supplying performance cannot necessarily be guaranteed even by applying vibration in this way.
Further, with the apparatus for supplying a constant quantity of abrasive 1 of the related art configured as described above, in order to prevent pressure inside the abrasive conduit 44 and the conduit for compressed air 46 from leaking to the inside of the abrasive tank 10, a slider 48 provided at an opening end edge of the abrasive conduit 44 is brought into sliding contact with the outer periphery of the drum 50, causing severe abrasion on the drum 50 and the slider 48, making frequent replacement necessary, and in particular since a boron member which is comparatively expensive is used as the slider running costs increase.
Further, if the abrasive that is the subject of supplying is left in a state where a large quantity of abrasive is collected and placed inside the tank 10, there may be instances where bridges occur and dry out as time elapses, and if bridges occur in this way, fluidity will be significantly impaired.
It therefore becomes difficult for the abrasive to enter into the grooves 47 and indented sections 49 because of the occurrence of bridges, accurate measurement of the abrasive becomes extremely difficult, and as a result, fluctuation arises in the quantity of abrasive supplied to the blast gun.
In particular, in the case where an elastic abrasive constituted by an elastic base material that is a dispersed mixture of abrasive formed to a specified grain diameter, or an elastic abrasive constituted by evenly supporting abrasive by fixing on the surface of an elastic base material formed to a specified grain diameter, is used as the abrasive, then it causes bridges to arise with this type of elastic material compared to the normal abrasive, and as a result, if blast processing is started or restarted after abrasive has been left inside the tank for a comparatively long time without being made to flow, then in the initial stages of starting or restarting the blast processing, the supplying quantity of abrasive is not constant and is unstable.
Fluidity varies with variation in the grain diameter of the abrasive, and as a result, in the event that the grain diameter of the abrasive is small and fluidity is comparatively good, there is an increase in the quantity of abrasive that is conveyed to the inside of the abrasive tank 10, and the level of abrasive inside the abrasive tank 10 becomes high. On the other hand, in order to prevent this as much as possible, a vibrator (not shown) for applying vibration to the known abrasive tank and a non-shown recovery tank is attached, and control of the vibrator is carried out to the recovery tank, but this is extremely difficult, and reduces fluidity, and lowers the supply level of abrasive in the abrasive tank 10. Further, a bridge phenomenon occurs in the branched conduit 42 and/or the abrasive conduit 44 blocking up corresponding parts, and a phenomenon arises where a supply level of abrasive becomes extremely unstable.
In the case of an apparatus for supplying a constant quantity of abrasive of the related art provided with a drum which is arranged not completely immersed within the abrasive, but in a state with partially exposed from the abrasive, if there is a fluctuation in the quantity of abrasive in the abrasive tank 10 in this way, there will be variations in the immersed state of the drum or the like, and variations in how the abrasive enters the grooves 47 accompanying variations in the quantity of abrasive in the abrasive tank, and if, for example, the drum is immersed at a comparatively deep position and the abrasive is evenly spread even at the periphery of the grooves 47, so that this type of spread abrasive increases the quantity of abrasive to be supplied together with abrasive inside the grooves 47, then accompanying variation in the grain diameter of abrasive that is the subject of supplying, variation in supplied abrasive quantity will arise.
Therefore, with an apparatus for supplying a constant quantity of abrasive of the related art provided with the above described structure, it is even necessary to give consideration to the particle diameter of abrasive used in order to accurately control overall quantity of abrasive to be supplied, and complicated control is required.
The present invention is made in view of the drawbacks above described related art, and an object of the present invention is to provide an apparatus for supplying a constant quantity of abrasive for a blasting machine that can make it easy to supply abrasive to hole sections and also make it easy to extract the abrasive from inside the hole sections, to thereby prevent fluctuation in the quantity of abrasive inside the hole sections during supplying to an abrasive conduit 44, thus enable accurate supplying of measured quantity of abrasive, and that can perform supplying a constant quantity of abrasive, and maintaining good fluidity even in the event that an abrasive that is prone to bridges, for example the previously described elastic abrasive, is used, and can supply a constant quantity of abrasive without being affected by fluctuation in the quantity of abrasive inside an abrasive tank accompanying fluctuation in the particle diameter of the abrasive in question.